The United Nations food agency has begun dropping food aid to rebel-held areas in central Sudan under a ceasefire agreement to allow humanitarian aid in to the stricken Nuba mountains region.

The UN World Food Programme (WFP) said 4,000 tonnes were to be delivered to the region - a stronghold of the Sudan People's Liberation Army (SPLA).

"In the first step, we are air dropping 324 tonnes to SPLA-controlled areas over the next 10 days. Overall, we will target 167,000 people in SPLA areas," WFP spokeswoman Laura Melo was quoted as saying.

She also said the agency was planning to deliver about 4,000 tonnes of food to more than 300,000 people in government-controlled areas in the region.

The WFP has been delivering food to southern Sudan since 1989.

It dropped some food aid to the Nuba mountains late last year during a temporary ceasefire.

Dire need

Sudan has been torn by 19 years of civil war, pitting the government in the mainly Muslim north against rebels in the mainly Christian and animist south.

The strife has killed an estimated two million people and uprooted four million more, and the UN says hundreds of thousands are in dire need of food aid.

In January, representatives of the government and the SPLA rebels signed a ceasefire agreement allowing aid workers access to the Nuba mountains.

At the end of last year, the WFP was able to make its first food drops to the region in more than a decade, following a temporary ceasefire negotiated by a US special envoy to Sudan.

But the agency is still unable to reach some other areas of conflict -in particular Western Upper Nile, where Sudan's oilfields are located.